Capacitive pressure sensor assembly

ABSTRACT

The disclosure is directed to a capacitive pressure sensor, and the assembly of a capacitive pressure sensor, that may be used within an implantable medical pump. In one example, a housing ferrule that encloses one capacitive plate and includes at least one protrusion for attaching a support structure of the capacitive plate. The at least one protrusion defines a smaller inner diameter as a reference point for securing the support structure while the ferrule provides a larger inner diameter to allow the support structure to tilt inside the ferrule to orient the capacitive plate into a desired plane. Despite manufacturing irregularities, the capacitive plate can be mounted in the desired plane parallel to another capacitive plate, a diaphragm, mounted to an edge of the ferrule. In another example, an assembly tool provides a stage to orient the capacitive plate and support structure within the ferrule at a desired depth.

TECHNICAL FIELD

The disclosure relates to pressure sensors and, more particularly, topressure sensors for use within implantable medical devices includingmedical pumps.

BACKGROUND

Medical pumps can be used to treat a variety of physiological,psychological, and emotional conditions. For some medical conditions,medical pumps can restore an individual to a more healthful conditionand a fuller life. For example, medical pumps may be used for chronicdelivery of therapeutic agents, such as drugs. As one specific example,a medical pump may be used to deliver insulin to a diabetic patient.Other examples include delivery of pain relief medication, e.g., to theintrathecal or epidural space of a patient, to alleviate chronic pain.

Some medical pumps are implantable. Implantable medical pumps areimplantable medical devices (IMDs) that may be implanted at a locationin the body of a patient and deliver a fluid medication through acatheter to a selected delivery site within the body of a patient.Typically, a catheter connects to an outlet of a medical pump outlet anddelivers a therapeutic agent at a programmed infusion rate to apredetermined location to treat a medical condition.

An implantable medical pump may be implanted by a clinician into apatient at a location that interferes as little as practicable withpatient activity. For example, implantable medical pumps are oftenimplanted subcutaneously in the lower abdomen of a patient. Implantablemedical pumps may include self-sealing fluid reservoirs accessiblethrough ports to facilitate in-service refilling by percutaneousinjection.

SUMMARY

In general, the disclosure describes an implantable medical pump with apressure sensor, and its assembly, for use within an implantable medicalpump. The pressure sensor may utilize changing capacitance between twocapacitive plates to detect changes in fluid pressure. One capacitiveplate may be rigid and disposed within a housing ferrule, and the othercapacitive plate may be a deflectable diaphragm mounted over one end ofthe housing ferrule.

A housing ferrule that encloses the rigid capacitive plate may include alip or protrusion for attaching a support structure of the capacitiveplate. The protrusion may provide a smaller inner diameter to attach thesupport structure while the housing ferrule may provide a larger innerdiameter that allows the support structure to tilt within the housingferrule. This tilting ability may enable the substantially rigidcapacitive plate to be oriented into to a desired plane. Despitepossible manufacturing irregularities, the rigid capacitive plate may bemounted in a plane parallel to a diaphragm capacitive plate mounted tothe distal edge of the ferrule.

In addition, an assembly tool provides a stage to orient the capacitiveplate and the support structure at a certain plane within the housingferrule at a desired distance from the distal edge of the housingferrule. The stage may be provided at a fixed height above the baseplate, and the stage may fit within the housing ferrule. Once thesupport structure is secured to the lip of the sensor housing, theassembly tool may be removed to allow the diaphragm to be attached tothe distal edge of the housing ferrule. In this manner, both capacitiveplates may be consistently positioned in parallel planes at a precisedistance apart from one another

In one example, a pressure sensor is described herein. The pressuresensor includes a housing ferrule defining a first inner diameter,wherein the housing ferrule is configured to receive a first capacitiveplate of a capacitor. The pressure sensor further includes at least oneprotrusion disposed within the housing ferrule that defines a secondinner diameter smaller than the first inner diameter. The at least oneprotrusion is configured to provide a mounting point between the housingferrule and a support structure of the first capacitive plate. Thehousing ferrule and the support structure define a gap when the at leastone protrusion is used to secure the support structure to the housingferrule. The housing ferrule is configured to support a secondcapacitive plate substantially parallel to the first capacitive platewithin the housing ferrule.

In another example, a method for assembling a pressure sensor isdescribed herein. The method includes placing a first capacitive plateand a support structure attached to the first capacitive plate within ahousing ferrule defining a first inner diameter. The method furtherincludes tilting the support structure within the housing ferrule toorient the first capacitive plate in a first plane substantiallyparallel to a second plane of a second capacitive plate. The methodfurther includes securing the support structure to the housing ferrulevia at least one protrusion, wherein the at least one protrusion definesa second inner diameter smaller than the first inner diameter. Themethod further includes mounting the second capacitive plate to thehousing ferrule.

In another example, a pressure assembly tool is described herein. Thetool includes a base plate. The tool further includes a stage raisedfrom the base plate. The stage is configured to fit within a housingferrule to allow an edge of the housing ferrule to pass the stage andcontact a top surface of the base plate. The stage is further configuredto set a uniform gap between a diaphragm plane defined by the edge ofthe housing ferrule and a capacitive plate mountable within the housingferrule.

In another example, a method for assembling a pressure sensor isdescribed herein. The method includes contacting an end of a housingferrule to a base plate of an assembly tool, wherein the housing ferrulesurrounds a stage of the assembly tool. The method further includesplacing a first capacitive plate and attached support structure withinthe housing ferrule. The method further includes placing the firstcapacitive plate against the stage to orient the first capacitive platein a first plane parallel to a second plane defined by the stage. Themethod further includes securing the support structure to the housingferrule. The method further includes mounting a second capacitive plateto the housing ferrule after removing the assembly tool.

The details of one or more aspects of the disclosure are set forth inthe accompanying drawings and the description below. Other features,objects, and advantages will be apparent from the description anddrawings, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a conceptual diagram illustrating one example of a fluiddelivery system that includes an implantable medical device (IMD) with amedical pump configured to deliver a therapeutic agent to a patient viaa catheter.

FIG. 2 is a functional block diagram illustrating an exemplary IMD witha medical pump.

FIG. 3 is a functional block diagram illustrating an exemplary externalprogrammer that communicates with an IMD.

FIG. 4 is a conceptual diagram illustrating one example of an IMDbulkhead configured to receive a pressure sensor consistent with thisdisclosure.

FIG. 5A is a conceptual diagram illustrating a cross-section of anotherexample of an IMD that includes a fluid enclosure defined by a pressuresensor and a bulkhead of an IMD consistent with this disclosure.

FIG. 5B is a conceptual diagram illustrating a cross-section of anotherexample of an IMD that includes a fluid enclosure defined by a pressuresensor and a bulkhead of an IMD consistent with this disclosure.

FIG. 6 is a conceptual diagram illustrating one example of a pressuresensor for use within an IMD consistent with this disclosure.

FIG. 7 is an exploded view of one example of a pressure sensorconsistent with this disclosure.

FIG. 8 is a conceptual diagram illustrating a top-down perspective viewof one example of a pressure sensor consistent with this disclosure.

FIG. 9 is a conceptual diagram illustrating a bottom-up perspective viewof one example of a pressure sensor including a diaphragm consistentwith this disclosure.

FIG. 10 is a conceptual diagram illustrating a cross-section of oneexample of a pressure sensor consistent with this disclosure.

FIG. 11 is a conceptual diagram illustrating one example of a mainhousing of a pressure sensor that includes a housing ferrule consistentwith this disclosure.

FIG. 12 is a conceptual diagram illustrating one example of afeedthrough assembly and a metal coating capacitive plate consistentwith this disclosure.

FIG. 13 is a conceptual diagram illustrating a cross-section of thefeedthrough assembly consistent with this disclosure.

FIG. 14 is a conceptual diagram illustrating one example of an assemblytool that may be used to set a capacitive gap of a pressure sensorconsistent with this disclosure.

FIG. 15 is a flow diagram illustrating one example of a method formounting a feedthrough assembly of a pressure sensor consistent withthis disclosure

FIG. 16 is a flow diagram illustrating one example of a method fororienting a pressure sensor within an IMD consistent with thisdisclosure.

FIG. 17 is a flow diagram illustrating one example of a method fordetecting a change in fluid quantity within a pressure sensor consistentwith this disclosure.

DETAILED DESCRIPTION

As described herein, this disclosure is directed to a pressure sensorfor use with medical devices. The pressure sensor may be a capacitivesensor that includes first and second capacitor plates, one of which maybe formed as a flexible diaphragm that deflects in response to changesin pressure. The pressure sensor may include a biocompatible and/orcorrosion resistant housing that houses the plates. The diaphragm may bepositioned such that one surface of the diaphragm contacts fluid to bemeasured. In this manner, the pressure sensor forms part of a fluidenclosure that is configured to accommodate and contact fluid within animplantable medical device (IMD), such as an implantable medical pumpthat delivers a drug to a patient. The pressure sensor may form at leasta portion of the fluid enclosure by contacting an adjacent fluidenclosure wall, for example, a fluid enclosure wall defined in abulkhead of the IMD. In this manner, operative portions of the pressuresensor comprise at least a portion of the pressure sensor packaginginstead of the pressure sensor being located within another packagingstructure. The fluid enclosure may be within the bulkhead or adjacent tothe bulkhead. The fluid enclosure may be utilized as a fluid channel forthe transfer of fluid within the IMD or as a fluid reservoir thatretains fluid within the IMD. In some examples, the pressure sensor mayhave a self-aligning shape and/or structure configured to receive thepressure sensor and align the sensor to a predetermined orientationwithin the fluid enclosure. The self-aligning shape may further serve toorient components of the sensor that provide electrical contacts forcoupling with other components of the IMD, e.g., electrical circuitry.

The capacitive pressure sensor may include a first capacitive plate thatis substantially rigid and a second capacitive plate that is deflectablein response to fluid pressure. The first capacitive plate may besubstantially rigid in the sense that it is configured to define astatic plane that acts as a reference such that a capacitance betweenthe first and second capacitive plates may be detected. The firstcapacitive plate may be formed by a metal coating on a rigid insulator.The first capacitive plate may be isolated from fluid by the secondcapacitive plate. The second capacitive plate may be formed of adiaphragm as described above. In some examples, the second capacitiveplate may be formed as a metal alloy diaphragm configured to be attachedto the pressure sensor housing. The pressure sensor may operate suchthat fluid pressure against the second capacitive plate causes thesecond capacitive plate to be deflected toward the first capacitiveplate, thereby causing a detectable capacitance between the plates. Inone example, a feedthrough pin may be coupled to the substantially rigidcapacitive plate recessed from the capacitive plane of the plate. Thefeedthrough pin may couple the first capacitive plate to a printedcircuit board or other circuitry of the pressure sensor. The secondcapacitive plate may be electrically coupled to the printed circuitboard via a housing of the pressure sensor.

The techniques of this disclosure are also directed to the assembly of apressure sensor. In one example, the pressure sensor includes a housingferrule configured to receive the first capacitive plate describedabove. The housing ferrule may include at least one protrusion definedwithin the housing ferrule. The at least one protrusion may present asupport structure for the mounting of the first, substantially rigid,capacitive plate within the housing ferrule. For example, the at leastone protrusion may provide a mounting point for affixing the firstcapacitive plate via welding or otherwise. The at least one protrusionmay be a single protrusion, a set of protrusions, an annular ring, alip, or other structure. The at least one protrusion may define asmaller diameter than a diameter of the housing ferrule, such that a gapis created between the housing ferrule and a support structure coupledto the first capacitive plate. The defined gap may to allow the supportstructure to tilt within the housing ferrule such that the capacitiveplate can be positioned in a plane parallel to an edge of the housingferrule. In one example, where the first, substantially rigid capacitiveplate is formed of a metal coating on a rigid insulator, it may bedesirable to tilt the support structure relative to the housing tocompensate for any discrepancy in a thickness of the metal coating. Anassembly tool may be used to facilitate the positioning of the rigidcapacitive plate by providing a stage at a fixed height within thehousing ferrule. Once the support structure is affixed in a secureposition within the ferrule, the assembly tool can be removed to allowthe second capacitive plate (e.g., flexible diaphragm) to be attached tothe distal edge of the housing ferrule.

The pressure sensor described herein may be used in several capacitieswithin the IMD. For example, the pressure sensor may be used to monitorthe fluid pressure of a refill port when fluid is being added to the IMDreservoir. In another example, the pressure sensor may be used tomonitor the pressure of fluid exiting the IMD and being delivered to apatient. As an additional example, the pressure sensor may be positionedto detect the pressure of a fluid within a reservoir retaining the fluidwithin the IMD. Further, two or more pressure sensors may be used tomonitor fluid pressure at several locations within the IMD. As describedherein, the fluid may generally in liquid form. Although generallydescribed for use within an implantable medical device, it iscontemplated that the pressure sensor described herein may be used inany other type of medical or non-medical systems or devices.

FIG. 1 is a conceptual diagram illustrating one example of a therapysystem 10 including an exemplary IMD 16 configured to deliver at leastone therapeutic agent, such as a pharmaceutical agent, insulin, painrelieving agent, anti-inflammatory agent, gene therapy agent, or thelike, to a target site within patient 12. The therapeutic agent may bedelivered via a catheter 18 coupled to IMD 16. In one example, catheter18 may comprise a plurality of catheter segments. In other examples,catheter 18 may be a unitary catheter. In the example shown in FIG. 1,the target site for fluid delivery is proximate to spinal cord 14 ofpatient 12. A proximal end 18A of catheter 18 is coupled to IMD 16,while a distal end 18B of catheter 18 is located proximate to the targetsite. Therapy system 10 also includes external programmer 20, whichwirelessly communicates with IMD 16 as needed, such as to provide orretrieve therapy information or control aspects of therapy delivery(e.g., modify the therapy parameters, turn IMD 16 on or off, receivewarnings or alerts, and so forth). While patient 12 is generallyreferred to as a human patient, other mammalian or non-mammalianpatients are also contemplated.

Generally, IMD 16 has an outer housing that is constructed of abiocompatible material that resists corrosion and degradation frombodily fluids, such as titanium or biologically inert polymers. IMD 16may be implanted within a subcutaneous pocket close to the therapydelivery site. For example, in the example shown in FIG. 1, IMD 16 isimplanted within an abdomen of patient 12. In other examples, IMD 16 maybe implanted within other suitable sites within patient 12 which maydepend, for example, on the target site within patient 12 for thedelivery of the therapeutic agent.

IMD 16 includes a medical pump that delivers fluid from a reservoir ofthe IMD to patient 12. As described herein, one or more pressure sensorsmay be employed within the IMD to monitor and detect pressures of fluidwithin IMD 16. The pressure sensors may detect static pressures alongwith pressure waves created when fluid is added or removed from the IMD.The pressure sensors may then provide information about the quantity offluid remaining within the IMD or delivered by the IMD.

Catheter 18 may be coupled to IMD 16 either directly or with the aid ofa catheter extension (not shown in FIG. 1). In the example shown in FIG.1, catheter 18 traverses from the implant site of IMD 16 to one or moretarget sites proximate to spine 14. Catheter 18 may be positioned suchthat one or more fluid delivery outlets of catheter 18 are proximate tothe one or more target sites within patient 12. IMD 16 may deliver atherapeutic agent to the one or more target sites proximate to spinalcord 14 with the aid of catheter 18. For example, IMD 16 may beconfigured for intrathecal drug delivery into the intrathecal space orepidural space surrounding spinal cord 14. The intrathecal space iswithin the subarachnoid space of spinal cord 14, which is past theepidural space and dura mater and through the theca of spinal cord 14.

Therapy system 10 may be used, for example, to reduce pain experiencedby patient 12. IMD 16 may deliver one or more therapeutic agents topatient 12 according to one or more dosing programs that set forthdifferent therapy parameters, such as a therapy schedule specifyingprogrammed doses, dose rates for the programmed doses, and specifictimes to deliver the programmed doses. The dosing programs may be a partof a program group for therapy, where the group includes a plurality ofdosing programs and/or therapy schedules. In some examples, IMD 16 maybe configured to deliver a therapeutic agent to patient 12 according todifferent therapy schedules on a selective basis. IMD 16 may include amemory to store one or more therapy programs, instructions defining theextent to which patient 12 may adjust therapy parameters, switch betweendosing programs, or undertake other therapy adjustments. Patient 12 mayselect and/or generate additional dosing programs for use by IMD 16 viaexternal programmer 20 at any time during therapy or as designated by aclinician.

In some examples, multiple catheters 18 may be coupled to IMD 16 totarget the same or different tissue or nerve sites within patient 12.Thus, although a single catheter 18 is shown in FIG. 1, in otherexamples, system 10 may include multiple catheters or catheter 18 maydefine multiple lumens for delivering different therapeutic agents topatient 12 or for delivering a therapeutic agent to different tissuesites within patient 12. Accordingly, in some examples, IMD 16 mayinclude a plurality of reservoirs for storing more than one type oftherapeutic agent. With multiple reservoirs, IMD 16 may include separatepressure sensors to monitor the fluid in each reservoir. In someexamples, IMD 16 may include a single long tube that contains thetherapeutic agent in place of a reservoir. However, for ease ofdescription, an IMD 16 including a single reservoir is primarilydiscussed herein with reference to the example of FIG. 1.

Programmer 20 may be an external computing device configured towirelessly communicate with IMD 16. For example, programmer 20 may be aclinician programmer that the clinician uses to communicate with IMD 16.Alternatively, programmer 20 may be a patient programmer that allowspatient 12 to view and modify therapy parameters. The clinicianprogrammer may include additional or alternative programming features,relative to the patient programmer. For example, more complex orsensitive tasks may only be allowed by the clinician programmer toprevent patient 12 from making undesired changes to the operation of IMD16.

Programmer 20 may be a hand-held computing device that includes adisplay viewable by the user and a user input mechanism that can be usedto provide input to programmer 20. For example, programmer 20 mayinclude a display screen (e.g., a liquid crystal display or a lightemitting diode display) that presents information to the user. Inaddition, programmer 20 may include a keypad, buttons, a peripheralpointing device, touch screen, voice recognition, or another inputmechanism that allows the user to navigate though the user interface ofprogrammer 20 and provide input.

In other examples, rather than being a handheld computing device or adedicated computing device, programmer 20 may be a larger workstation ora separate application within another multi-function device. Forexample, the multi-function device may be a cellular phone, personalcomputer, laptop, workstation computer, or personal digital assistantthat can be configured to an application to simulate programmer 20.Alternatively, a notebook computer, tablet computer, or other personalcomputer may execute an application to function as programmer 20, e.g.,with a wireless adapter connected to the personal computer forcommunicating with IMD 16.

A clinician may use programmer 20 to program IMD 16 with one or moretherapy programs that define the therapy delivered by IMD 16. During aprogramming session, the clinician may determine one or more dosingprograms that may provide effective therapy to patient 12. Patient 12may provide feedback to the clinician as to the efficacy of a specificprogram being evaluated or desired modifications to the dosing program.Once the clinician has identified one or more programs that may bebeneficial to patient 12, patient 12 may continue the evaluation processand determine which dosing program or therapy schedule best alleviatesthe condition of patient 12 or otherwise provides efficacious therapy topatient 12.

The dosing program information may set forth therapy parameters, such asdifferent predetermined dosages of the therapeutic agent (e.g., a doseamount), the rate of delivery of the therapeutic agent (e.g., rate ofdelivery of the fluid), the maximum acceptable dose, a time intervalbetween successive supplemental doses such as patient-initiated doses(e.g., a lock-out interval), a maximum dose that may be delivered over agiven time interval, and so forth. IMD 16 may include a feature thatprevents dosing the therapeutic agent in a manner inconsistent with thedosing program. Programmer 20 may assist the clinician in thecreation/identification of dosing programs by providing a methodicalsystem of identifying potentially beneficial therapy parameters.

A dosage of a therapeutic agent, such as a drug, may be expressed as anamount of drug, e.g., measured in milligrams, provided to the patientover a particular time interval, e.g., per day or twenty-four hourperiod. This dosage amount may convey to the caregiver an indication ofthe probable efficacy of the drug and the possibility of side effects ofthe drug. In general, a sufficient amount of the drug should beadministered in order to have a desired therapeutic effect, such as painrelief. However, the amount of the drug administered to the patient maybe limited to a maximum amount, such as a maximum daily dose, in ordernot to avoid potential side effects. Program information specified by auser via programmer 20 may be used to control dosage amount, dosagerate, dosage time, maximum dose for a given time interval (e.g., daily),or other parameters associated with delivery of a drug or other fluid byIMD 16.

In some cases, programmer 20 may also be configured for use by patient12. When configured as a patient programmer, programmer 20 may havelimited functionality in order to prevent patient 12 from alteringcritical functions or applications that may be detrimental to patient12. In some cases, a patient programmer may permit the patient tocontrol IMD 16 to deliver a supplemental, patient-initiated dose, ifpermitted by the applicable therapy program administered by the IMD,e.g., if delivery of a patient-initiated dose would not violate alockout interval or maximum dosage limit. Programmer 20 may also providean indication to patient 12 when therapy is being delivered or when IMD16 needs to be refilled or when the power source within programmer 20 orIMD 16 need to be replaced or recharged.

Programmer 20 may also provide warnings or alerts to the clinician orpatient to indicate when there is a problem with an aspect of IMD 16.For example, programmer 20 may provide a visual and/or audible alertwhen the pressure sensor detects beyond threshold pressure near therefill port. In this manner, the clinician may avoid damaging fluidenclosures, the pressure sensor, or other components of IMD 16 as wellas preventing an overflow of drug into patient 12. In another example,programmer 20 may relay an alert when the pressure sensor detects abovethreshold pressures within the fluid enclosure that indicate a blockageto the delivery of drug to patient 12.

Programmer 20 may also alert a user that an unauthorized removal offluid has occurred. For example, the pressure sensor may be capable ofdetecting movement or changes in the quantity of the fluid separate fromthe operation of the medical pump. In this manner, IMD 16 may be able toidentify when fluid has been removed from IMD 16 without an instructedor authorized delivery of fluid to patient 12. IMD 16 may transmit thealert to programmer 20, and programmer 20 may present the alert to auser, e.g., a clinician. Whether external programmer 20 is configuredfor clinician or patient use, programmer 20 may communicate to IMD 16 orany other computing device via wireless communication. Programmer 20,for example, may communicate via wireless communication with IMD 16using radio frequency (RF) telemetry techniques known in the art.Programmer 20 may also communicate with another programmer or computingdevice via a wired or wireless connection using any of a variety oflocal wireless communication techniques, such as RF communicationaccording to the 802.11 or Bluetooth specification sets, infrared (IR)communication according to the IRDA specification set, or other standardor proprietary telemetry protocols. Programmer 20 may also communicatewith another programming or computing device via exchange of removablemedia, such as magnetic or optical disks, or memory cards or sticks.Further, programmer 20 may communicate with IMD 16 and anotherprogrammer via remote telemetry techniques known in the art,communicating via a local area network (LAN), wide area network (WAN),public switched telephone network (PSTN), or cellular telephone network,for example.

In other applications of therapy system 10, the target therapy deliverysite within patient 12 may be a location proximate to sacral nerves(e.g., the S2, S3, or S4 sacral nerves) in patient 12 or any othersuitable nerve, organ, muscle or muscle group in patient 12, which maybe selected based on, for example, a patient condition. For example,therapy system 10 may be used to deliver a therapeutic agent to tissueproximate to a pudendal nerve, a perineal nerve or other areas of thenervous system, in which cases, catheter 18 would be implanted andsubstantially fixed proximate to the respective nerve. As furtherexamples, catheter 18 may be positioned to deliver a therapeutic agentto help manage peripheral neuropathy or post-operative pain mitigation,ilioinguinal nerve therapy, intercostal nerve therapy, gastricstimulation for the treatment of gastric motility disorders and/orobesity, muscle stimulation, for mitigation of other peripheral andlocalized pain (e.g., leg pain or back pain). As another example,catheter 18 may be positioned to deliver a therapeutic agent to a deepbrain site or within the heart (e.g., intraventricular delivery of theagent). Delivery of a therapeutic agent within the brain may help manageany number of disorders or diseases. Example disorders may includedepression or other mood disorders, dementia, obsessive-compulsivedisorder, migraines, obesity, and movement disorders, such asParkinson's disease, spasticity, and epilepsy. Catheter 18 may also bepositioned to deliver insulin to a patient with diabetes.

Examples of therapeutic agents that IMD 16 may be configured to deliverinclude, but are not limited to, insulin, morphine, hydromorphone,bupivacaine, clonidine, other analgesics, genetic agents, antibiotics,nutritional fluids, analgesics, hormones or hormonal drugs, gene therapydrugs, anticoagulants, cardiovascular medications or chemotherapeutics.

FIG. 2 is a functional block diagram illustrating components of anexample of IMD 16, which includes processor 22, memory 24, pressuresensor 26, refill port 28, reservoir 30, internal tubing 32, catheteroutlet 36, medical pump 38, power source 40, and telemetry module 42.Medical pump 38 may be a mechanism that delivers a therapeutic agent insome metered or other desired flow dosage to the therapy site withinpatient 12 from reservoir 30 via the catheter 18. Refill port 28 maycomprise a self-sealing injection port. The self-sealing injection portmay include a self-sealing membrane to prevent loss of therapeutic agentdelivered to reservoir 30 via refill port 28. After a delivery system,e.g., a hypodermic needle, penetrates the membrane of refill port 28,the membrane may seal shut when the needle is removed from refill port28. Internal tubing 32 may be a segment of tubing that runs fromreservoir 30, around or through medical pump 38 to catheter outlet 36.Internal tubing 32 may be constructed of any materials capable offorming a fluid path or fluid enclosure, such as cavities within metalstructures or adjoined structures that form continuous surfaces toaccommodate fluid.

Pressure sensor 26 may monitor a pressure of fluid within a fluidenclosure of IMD 16. This fluid enclosure may be part of internal tubing32, e.g., adjacent to catheter outlet 36, reservoir 30, or refill port28. In the example of FIG. 2, pressure sensor 26 is positioned to createa portion of the fluid enclosure defining reservoir 30. In this manner,pressure sensor 26 includes diaphragm that contacts the fluid withinreservoir 30 and seals electrical components from the fluid. Thediaphragm operates as one capacitive plate of the pressure detectingcapacitor. Circuitry of IMD 16 may detect changes in fluid pressurebased on a detected change in capacitance between the diaphragm andanother capacitive plate contained within a housing of pressure sensor26. Pressure sensor 26 may utilize energy from a power source 40 tocause an electrical potential between the diaphragm and substantiallyrigid capacitor plate.

As pressure sensor 26 detects changes in capacitance from diaphragmdeflection, pressure sensor 26 may communicates with a processor 22and/or other circuitry to transmit data or signals (e.g., indicative ofa detected capacitance) representative of detected fluid pressure. Inone example, a flex circuit (not shown) may be used to electricallycouple pressure sensor 26 to processor 22. Processor 22 may accordinglyadjust IMD 16 function or transmit information to a user based uponreceived information indicative of detected fluid pressure. In addition,medical pump 38 may communicate directly to pressure sensor 26 toretrieve pressure information.

In the example of FIG. 2, pressure sensor 26 delivers pressureinformation to processor 22 periodically or upon request by processor22. Pressure sensor 26 may internally calibrate the measured capacitancevalues and output a voltage, or digital, signal indicative of a detectedpressure. Processor 22 may then use this signal to identify the detectedpressure at the diaphragm. In one example, an analog to digitalconverter of IMD 16 may convert an analog voltage signal indicative ofdetected pressure from pressure sensor 26 to a digital valuerepresentative of the detected fluid pressure. Processor 22 may processthis digital value and apply an algorithm or look-up table to generatecalibrated pressure of the fluid. This processed pressure value may thenbe usable by software controlling operation of IMD 16 via processor 22.

Pressure sensor 26 may convert detected capacitance between the rigidcapacitor plate and the diaphragm capacitor plate differently thanconventional parallel plate capacitors due to the shape of the diaphragmwith fully constrained edges. In the example of a circular diaphragm asdescribed herein, the capacitance gap is the smallest at the center andincreased toward the diaphragm edge. Factors such as the ambienttemperature, permittivity of free space, in-plane tension on thediaphragm, elasticity of the diaphragm material, diaphragm thickness,and the radius of the rigid capacitor may relevant to the measuredcapacitance. Some of these factors may be less relevant withnon-circular diaphragms. In other examples, capacitance measurements maybe developed experimentally to create a formula or look-up table thatdetermines pressure-capacitance relationships. This look-up table orformula may be stored in pressure sensor 26 or in memory 24.

Although only a single pressure sensor 26 is depicted in the example ofFIG. 2, multiple pressure sensors may be provided within IMD 16. In oneexample, the multiple pressure sensors may be positioned to detectpressure within different fluid enclosures. For example, a pressuresensor may be positioned within a fluid channel between refill port 28and reservoir 30 and another pressure sensor may be positioned within afluid channel between medical pump 38 and catheter outlet 36. In anotherexample, a pressure sensor may be positioned within a fluid enclosurethat creates reservoir 30, a second pressure sensor may be positionedwithin a fluid channel adjacent refill port 28, and a third pressuresensor may be positioned within a fluid channel adjacent catheter outlet36. These and other multiple pressure sensor configurations arecontemplated with the pressure sensor disclosed herein. Alternatively,multiple pressure sensors may be placed within the same fluid enclosurein order to provide redundant sensors in the case of a malfunction.Further, multiple pressure sensors may be utilized within the same fluidenclosure to provide more detailed information indicative of detectedpressure that may be capable of identifying a quantity or velocity of afluid dispensed by medical pump 38. Any pressure sensors within IMD 16may be monitored and/or controlled by processor 22 and/or othercircuitry of IMD 16.

In other examples, pressure sensor 26 may employ two or more capacitorsfor detecting fluid pressure at different locations within one fluidenclosure or multiple different fluid enclosures. In this manner,pressure sensor 26 may include multiple diaphragms that each form acapacitive pressure sensor with an associated substantially rigidcapacitive plate.

Processor 22 may controls the operation of medical pump 38 with the aidof instructions associated with program information that is stored inmemory 24. For example, the instructions may define dosing programs thatspecify an amount of a therapeutic agent to be delivered to a targettissue site within patient 12 from reservoir 30 via catheter 18. Theinstructions may further specify a time at which the agent will bedelivered and the time interval over which the agent will be delivered.The amount of the agent and the time over which the agent will bedelivered may be functions of a dosage rate at which fluid is delivered.In other examples, a quantity of the agent may be delivered according toone or more physiological characteristics of a patient, e.g.,physiological characteristics sensed by one or more sensors (not shown)implanted within a patient as part of therapy system 10 (FIG. 1).Components described as processors within IMD 16 and external programmer20 may each comprise one or more processors, such as one or moremicroprocessors, digital signal processors (DSPs), application specificintegrated circuits (ASICs), field programmable gate arrays (FPGAs),programmable logic circuitry, or the like, either alone or in anysuitable combination.

Memory 24 may include any volatile or non-volatile media, such as arandom access memory (RAM), read only memory (ROM), non-volatile RAM(NVRAM), electrically erasable programmable ROM (EEPROM), Flash memory,and the like. As mentioned above, memory 24 may store programinformation including instructions for execution by processor 22, suchas, but not limited to, therapy programs, historical therapy programs,timing programs for delivery of fluid from reservoir 30 to catheter 18,and any other information regarding therapy of patient 12. In addition,memory 24 may store instructions for the operation of pressure sensor26, such as maximum pressure thresholds, calibration algorithms, andcapacitance formulas. Further, memory 24 may contain instructions foroperations upon certain fluid pressures being detected. Memory 40 mayinclude separate memories for storing instructions, patient information,therapy parameters (e.g., grouped into sets referred to as “dosingprograms”), therapy adjustment information, program histories, and othercategories of information such as any other data that may benefit fromseparate physical memory modules.

Telemetry module 42 in IMD 16, as well as telemetry modules in acontroller, such as programmer 20, may accomplish communication by RFcommunication techniques. In addition, telemetry module 42 maycommunicate with programmer 20 via proximal inductive interaction of IMD16 with external programmer 20. In one example, processor 22 controlstelemetry module 42 to send and receive information.

Power source 40 delivers operating power to various components of IMD16. Power source 40 may include a small rechargeable or non-rechargeablebattery and a power generation circuit to produce the operating power.In the case of a rechargeable battery, recharging may be accomplishedthrough proximal inductive interaction between an external charger andan inductive charging coil within IMD 16. In some examples, powerrequirements may be small enough to allow IMD 16 to utilize patientmotion and implement a kinetic energy-scavenging device to tricklecharge a rechargeable battery. In other examples, traditional batteriesmay be used for a limited period of time. As a further alternative, anexternal inductive power supply may transcutaneously power IMD 16whenever measurements are needed or desired.

FIG. 3 is a functional block diagram illustrating various components ofan example external programmer 20 for IMD 16. As shown in FIG. 3,external programmer 20 is an external display device that includesprocessor 44, memory 48, telemetry circuit 50, user interface 46, andpower source 52. External programmer 20 may be embodied as a patientprogrammer or clinician programmer. A clinician or patient 12 interactswith user interface 46 in order to manually change the stimulationparameters of a program, change programs within a group, view therapyinformation, receive warnings or alerts, or otherwise interact with andcontrol IMD 16. Generally, external programmer 20 configured as aclinician programmer have include additional features not provided onthe patient programmer.

User interface 46 may include a screen or display and one or more inputbuttons that allow external programmer 20 to receive input from a user.Alternatively, user interface 46 may additionally or only utilize atouch screen display. The screen may be a liquid crystal display (LCD),dot matrix display, organic light-emitting diode (OLED) display, touchscreen, or any other device capable of delivering and/or acceptinginformation. For audible and/or tactile indications, such as an abovethreshold pressure, external programmer 20 may further include one ormore audio speakers, voice synthesizer chips, piezoelectric buzzers, orthe like.

Input buttons for user interface 46 may include a touch pad, increaseand decrease buttons, emergency shut off button, and other buttonsneeded to control the delivery of drug therapy. Processor 44 controlsuser interface 46, retrieves data from memory 48 and stores data withinmemory 48. Processor 44 also controls the transmission of data throughtelemetry circuit 50 to IMD 16. Memory 48 includes operationinstructions for processor 44 and data related to patient 12 therapy.

Telemetry circuit 50 allows the transfer of data to and from IMD 16.Telemetry circuit 50 may communicate with IMD 16 in real-time duringdrug refill or certain communication tasks. For example, IMD 16 mayimmediately transmit an alert if pressure sensor 26 indicates an abovethreshold pressure in reservoir 30 that could be indicative of ablockage in catheter 18.

In addition, telemetry circuit 50 may communicate at a scheduled time orwhen the telemetry circuit detects the proximity of IMD 16. Userinterface 46 may then update displayed information accordingly.Alternatively, telemetry circuit 50 may communicate with IMD 16 whensignaled by a user through user interface 46. To support RFcommunication, telemetry circuit 50 may include appropriate electroniccomponents, such as amplifiers, filters, mixers, encoders, decoders, andthe like. Power source 52 may be a rechargeable battery, such as alithium ion or nickel metal hydride battery. Other rechargeable orconventional batteries may also be used. In some cases, externalprogrammer 20 may be used when coupled to an alternating current (AC)outlet, i.e., AC line power, either directly or via an AC/DC adapter.

In some examples, external programmer 20 may be configured to rechargeIMD 16 in addition to programming IMD 16. Alternatively, a rechargingdevice may be capable of communication with IMD 16. Then, the rechargingdevice may be able to transfer programming information, data, or anyother information described herein to IMD 16. In this manner, therecharging device may be able to act as an intermediary communicationdevice between external programmer 20 and IMD 16. In other cases,programmer 20 may be integrated with a recharging functionality in thecombined programming/recharging device. The techniques described hereinmay be communicated between IMD 16 via any type of external devicecapable of communication with IMD 16.

FIG. 4 is a conceptual diagram illustrating one example of a bulkhead104 of IMD 100. IMD 100 is similar to IMD 16 of FIGS. 1 and 2, but FIG.4 shows selected components housed within an exposed bulkhead 14. Theexample of FIG. 4 shows that IMD 100 includes reservoir back housing102, bulkhead 104, circuitry 106, refill port 105, refill opening 110,catheter access port 108, pressure sensors 112A and 112B (collectively“pressure sensors 112”), flexible circuit 114, and catheter 18. Abulkhead cover (not shown) has been removed to show these components.The bulkhead cover may be provided to seal the electrical componentsfrom body fluids and tissues of patient 12. In some examples, thebulkhead cover may be integrated with bulkhead 104.

In addition, some components that are hidden under bulkhead 104 are alsoshown using dotted lines. These components describe an example fluidpath within the example of FIG. 4. Fluid channel 107A provides a pathfor fluid between refill port 105 and pressure sensor 112A. Fluidchannel 107BA provides a path for fluid between pressure sensor 112A andreservoir 103. Together, fluid channels 107A and 107B (collectively“fluid channel 107”) create a fluid path for fluid to refill reservoir103. Fluid channel 107A may be a fluid enclosure that is a portion of areceptacle for receiving fluid within IMD 100. Pressure sensor 112A thusdetects the pressure of fluid between refill port 105 and reservoir 103.

Fluid channels 111A, 111B, 111C, and 111D (collectively “fluid channels111”) create a fluid path for fluid to be dispensed from reservoir 103and delivered to patient 12. Fluid channel 111A connects reservoir 103to medical pump 109. Fluid channel 111B provides a fluid path betweenmedical pump 109 and catheter access port 108. Fluid channel 111Cprovides a fluid path between catheter access port 108 and pressuresensor 112B, and fluid channel 111D provides a fluid path betweenpressure sensor 112B and catheter 18, via the catheter outlet (notshown). Pressure sensor 112B thus detects the pressure of fluid betweenmedical pump 109 and catheter 18. In other examples of IMD 100, apressure sensor may also be positioned to detect the pressure of thefluid within reservoir 103. In this manner, a fluid enclosure may takeon different forms. Fluid channels 107 and 111 are both fluid enclosuresthat allow a fluid to flow through the structure. Conversely, reservoir103 may be a fluid enclosure that is configured to retain or store fluidfor later delivery to patient 12.

Reservoir back housing 102 encloses the portion of IMD 100 that retainsa fluid, e.g., a delivered medication, within IMD 100. Reservoir backhousing 102 may also be mated to bulkhead 104 to form hermitic seal ofIMD 100. The hermetic seal may isolate components of IMD 100 from theenvironment in which IMD 100 is disposed. Bulkhead 104 may also form aportion of a fluid enclosure wall that contacts fluid within thereservoir. Bulkhead 104 may also form a portion of an external surfaceof IMD 100 that contacts patient 12 tissues when implanted.

Bulkhead 104 may house functional components of IMD 100. For example,bulkhead 104 may include refill port 105 and refill opening 110 toaccept a syringe to replenish a drug to be later delivered to patient12. Refill opening 110 may help to guide a syringe into a diaphragm thataccepts a needle of the syringe to aid the clinician in refilling IMD100 when IMD is disposed within patient 12.

Pressure sensors 112 of FIG. 4 illustrate examples of pressure sensor 26as illustrated in FIG. 2. Pressure sensors 112 may be mounted withinopenings defined by bulkhead 104 to form a portion of a fluid enclosurein which each pressure sensor 112 detects fluid pressure. Pressuresensor 112A may be positioned to define at least a portion of fluidchannel 107 that directs fluid between refill port 105 and reservoir 103of IMD 100, and pressure sensor 112B may be positioned to define thefluid channel 111 that directs fluid between medical pump 109 andcatheter 18 of IMD 100. When fluid is added within refill opening 110,the fluid passes through channel 107 and into reservoir 103.

In one example, pressure sensors 112 are identical to each other in sizeand shape as well as pressure sensing function. In other examples,pressure sensors 112 may be of different size, shape, and/or pressuresensing function. In examples where pressure sensor 112A may beidentical to pressure sensor 112B, either pressure sensor can be used ateach location, thereby simplifying and construction of IMD 100. In oneexample, one or both of pressure sensors 112 may also have aself-aligning shape that positions each pressure sensor in apredetermined orientation within the channel opening of bulkhead 104.The self-aligning shape of each pressure sensor 112 may also facilitateelectrical contact between pressure sensors 112 and flexible circuit 114for coupling of pressure sensors 112 to one or more circuits of IMD 100,e.g., circuit 106 depicted in FIG. 4. In other words, the predeterminedorientation may position one or more electrical contacts of one or moreof pressure sensors 112 in proximity to flexible circuit 114 forelectrical coupling to circuitry 106 and/or other circuitry of IMD 100.Flexible circuit 114 as described herein may by any structure capable oftransferring electrical energy, e.g., signal indicative of detectedpressure measurements. For example, flex circuit 114 may be a PC boardtrace, electrically conductive tape, or any other like structure.

Circuitry 106 may recognize in which fluid enclosure each of pressuresensors 112 detects fluid pressure within IMD 16 based upon whichconnection channel of flexible circuit 114 each pressure sensor uses.Circuitry 106 may include a processor and memory, e.g., processor 22 andmemory 24 of IMD 16 in FIG. 2, and communicate with one or more ofpressure sensors 112, e.g., to receive one or more indications of fluidpressure measurements. Flexible circuit 114 may be electrically coupledto circuitry 106 and/or pressure sensors 112. Flexible circuit 114 maybe configured to connect with the electrical connections of pressuresensors 112, and flexible circuit 114 may include separate channels forcommunications between circuitry 106 and pressure sensors 112.

Other components may also be provided within bulkhead 104. For example,bulkhead 104 may house a telemetry circuit, a power supply, a medicalpump, and other components desirable for the deliver drug therapy topatient 12.

FIG. 5A is a conceptual diagram illustrating a cross-section of oneexample of an IMD 16 that includes a pressure sensor 112. As shown inFIG. 5A, IMD 16 includes reservoir back housing 102, bulkhead 104,pressure sensor 112, flexible circuit 114, top shield 116, valve 118,and components 120. Pressure sensor 112 may be any pressure sensordescribed herein, such as the example pressure sensor 26 depicted inFIG. 2. Components 120 may include various electrical and structuralcomponents required for the function of IMD 16, such as a processor,power supply, memory, telemetry circuitry, and medical pump controls.The medical pump that delivers fluid from IMD 16 is not shown in FIG.5A.

Reservoir back housing 102 may be mated and/or sealed to bulkhead 104.Bulkhead 104 may define a fluid enclosure wall, or a portion of a fluidenclosure wall, that defines a portion of reservoir 122 accommodating orretaining the fluid. Reservoir 122 is an example fluid enclosure thatcontains, retains or channels fluid within IMD 16. Reservoir 122 may bedefined by pressure sensor 112 and reservoir bellows 128. In oneexample, pressure sensor 112 includes an operative surface that contactsa fluid within reservoir 122 and attaches to bulkhead 104 to form acontinuous surface. In this manner, pressure sensor 112 may physicallycontact bulkhead 104 or attach to bulkhead 104 with a weld or othermechanism for completing a surface defining reservoir 122. Reservoirbellows 128 may expand and contract in response to a volume of fluidaccommodated by reservoir 122. Remaining capacity 124 is the spacebetween reservoir bellows 128 and reservoir back housing 102. In oneexample, reservoir bellows 128 may be constructed of a folding structurethat unfolds to increase the volume of fluid accommodated by channel122. Alternatively, reservoir bellows 128 is an elastic barrier made ofa polymer or other flexible biocompatible and/or non-corrosive materialthat allows fluid to be removed from reservoir 122 and delivered topatient 12. In other examples, reservoir 128 may be partially defined byanother structure different than reservoir bellows 128. In someexamples, a propellant or other gas may reside in remaining capacity 124to provide back pressure to reservoir bellows 128.

Valve 118 may positioned within bulkhead 104 and configured to fullyenclose reservoir 122. Valve 118 may be controlled to allow fluid toenter medical pump 38 (not shown). Alternatively, valve 118 may be partof a medical pump 38 that allows fluid to leave reservoir 122 and bedelivered to patient 12. In other examples of IMD 16, medical pump 38may function as valve 118 by only allowing fluid to leave reservoir 122upon operation of medical pump 38. In any case, valve 118 may operate toclose reservoir 122 defined by bulkhead 104 and pressure sensor 112.

Pressure sensor 112 may be configured to detect the pressure of fluidretained within reservoir 122. Since the deformable diaphragm (not shownin FIG. 5A) of pressure sensor 112 forms a portion of the fluidenclosure wall defining reservoir 122, pressure sensor 112 is capable ofdetecting a pressure of fluid within reservoir 122 or any pressurechange caused by the addition or removal of fluid from the fluidenclosure. Pressure sensor 112 may also have a self-aligning shape toocclude, and reside at least partially within, a channel opening inbulkhead 104. Although pressure sensor 112 may fully occlude the channelopening when inserted, other examples may require pressure sensor 112 tobe welded at the joint between bulkhead 104 and pressure sensor 112before the channel opening is fully occluded to form a sealed barrier tofluid. As shown in FIG. 5A, the channel opening is defined by bulkhead104 where pressure sensor 112 resides. The channel opening may be sizedand/or shaped to only accept pressure sensor 112 in a predeterminedorientation. In another example, the channel opening may include a keyedstructure to only accept pressure sensor 112 in a predeterminedorientation. Upon the installation of pressure sensor 112 into bulkhead104, reservoir 122 is completed, i.e., pressure sensor 112 forms atleast one surface of reservoir 122.

In the example of FIG. 5A, pressure sensor 112 includes housing ferrule156 which provides an attachment structure for the diaphragm and anenclosure for a rigid capacitive plate. Housing ferrule 156 as depictedin FIG. 5A is substantially cylindrical, however other shapes (e.g.,oval, square, rectangular, other) are also contemplated and consistentwith this disclosure. As depicted in FIG. 5A, housing ferrule 156extends from bulkhead 104 and into reservoir 122. In other examples notdepicted in FIG. 5A, pressure sensor 112 may be configured differently.For example, the deformable diaphragm may be welded flush with thesurface of pressure sensor 112 such that housing ferrule 156 does notextend into reservoir 122. In this manner, housing ferrule 156 mayreside within pressure sensor 112. In other examples, housing ferrule156 may be recessed within pressure sensor 112 to provide an indent orcavity. According to these examples, bulkhead 104 and pressure sensor112 in combination may provide a continuous surface that definesreservoir 122.

In addition to bulkhead 104 forming a portion of reservoir 122, bulkhead104 may also support other components 120 of IMD 16. Components 120 maybe mounted to or formed of bulkhead 104, and/or components 120 mayreside within a space defined by bulkhead 126. For example, flexiblecircuit 114 may be coupled to pressure sensor 112 and a processor of IMD16. Bulkhead space 126 may be defined by bulkhead 104, and may also bedefined by top shield 116. Top shield 116 may mate with bulkhead 104form a hermetic enclosure that protects components 120 within bulkheadspace 126 from body tissues and fluids when IMD 16 is implanted withinpatient 12.

Together, top shield 116, bulkhead 104, and reservoir back housing 102forms the exterior surface of IMD 16. In other examples, the exteriorsurface of IMD 16 may be formed by fewer components. For example,bulkhead 104 may reside completely within top shield 116. In otherwords, top shield 116 may mate to reservoir back housing 102 to createthe exterior surface of IMD 16. Bulkhead 104 may then mount within topshield 116 or reservoir back housing 102.

Reservoir back housing 102, bulkhead 104, and top shield 116 may beconstructed of biocompatible and/or corrosion-resistant materialsbecause their surfaces come into contact with corrosive drugs, bodilyfluids, or both. In some examples, the materials may only need to benon-corrosive and compatible with pharmacological agents, and notbiological agents, to function within the example of FIG. 5A. Examplematerials include polymers, ceramics, composite materials, and metalalloys. Example metal alloys include stainless steel, aluminum alloys,and titanium alloys. Example titanium alloys include Grades 1, 2, 5, or9 titanium. Although the same material may be used to form each ofreservoir back housing 102, bulkhead 104, and top shield 116, differentmaterials may also be used.

Although reservoir 122 is a reservoir for fluid as depicted in theexample of FIG. 5A, pressure sensor 112 may be utilized to detectpressure in other types of fluid enclosures as well. For example thefluid enclosure may be a conduit that accommodates fluid from the refillport to the reservoir. In other examples, the fluid enclosure may be aconduit that accommodates fluid between the reservoir and the exit portof IMD 16. In this manner, pressure sensor 112 may form a portion of anyfluid enclosure that retains or directs fluid within IMD 16. In anexample where reservoir 122 is a conduit within bulkhead 104, allsurrounding surfaces of bulkhead 104 that define at least a portion ofthe fluid enclosure may be considered a fluid enclosure wall, becausebulkhead 104 defines at least a portion of a barrier defining the fluidenclosure.

FIG. 5B is a conceptual diagram illustrating a cross-section of examplefluid channel 132 defined by pressure sensor 112 and bulkhead 104B.Fluid channel 132 is one example of a fluid enclosure. As shown in FIG.5B, bulkhead 104B may provide a recessed mounting position for pressuresensor 112. Plate 130 may be attached to bulkhead 104B via one or moreof a fastener, adhesive, weld, and/or any other attachment mechanism.Pressure sensor 112, plate 130, and bulkhead 104B may act as fluidenclosure walls that define fluid channel 132 within bulkhead 104B. Inthis manner, fluid channel 132 is one example of a fluid enclosurewithin bulkhead 104B that is capable of retaining fluid, or drug, insideIMD 16, for example. Fluid channel 132 may be a pathway that directsfluid from a reservoir to a pump mechanism, from a pump mechanism to anoutput port, or a refill port to a reservoir. As fluid is retained in ormoves through fluid channel 132, pressure sensor 112 may detect thepressure of the fluid. This pressure may also be used to indicate theflow rate of the fluid.

Bulkhead 104B may separate a fluid reservoir (not shown in FIG. 5B) fromelectrical components housed within IMD 16. Bulkhead 104B may be similarto bulkhead 104A of FIG. 5A with the difference that bulkhead 104B doesnot directly expose pressure sensor 112 to fluid of the IMD 16reservoir. The distance between pressure sensor 112 and plate 130 maygenerally be between approximately 0.1 mm and 10 mm. However, smaller orlarger distances are also contemplated based upon the application inwhich pressure sensor 112 is intended. Smaller distances, and smallervolumes of fluid channel 132, may facilitate fluid flow functions whilelarger distances may facilitate fluid holding functions. In otherexamples, both bulkhead 104B and plate 130 may be manufactured from asingle piece of material so that only bulkhead 104B and the externalsurface of pressure sensor 112 form the fluid enclosure walls of fluidchannel 132.

FIG. 6 is a conceptual diagram illustrating one example of a pressuresensor 112 for use within IMD 16. As shown in FIG. 6, pressure sensor112 includes sensor housing 150, printed circuit board 152, andfeedthrough pin 154. Housing ferrule 156 may be a portion of sensorhousing 150 that extends with respect to the rest of sensor housing 150.Although housing ferrule 156 is cylindrical, other examples of pressuresensor 112 may provide a housing ferrule of other shapes such as arectangle, square, and/or oval shape.

Sensor housing 150 may be shaped to self-align into an opening ofbulkhead 104 sized and shaped to accept sensor housing 150. Althoughsensor housing 150 is eccentrically shaped in the example of FIG. 6,sensor housing 150 may instead be configured into any shape that allowspressure sensor 112 to self-align to a similarly shaped opening inbulkhead 104. An eccentric shape may generally be a non-circular shape.For example, a tear-drop shape or the shape of sensor housing 150 inFIG. 8 may be considered an eccentric shape. For the purposes of thisdisclosure, an eccentric shape is any structure that can only be matchedto a similarly shaped opening in one position when rotated 360 degrees.These other shapes may include rounded shapes with notches orprotrusions that “key” the orientation of pressure sensor 112 tobulkhead 104.

Printed circuit board 152 may also be shaped to fit within sensorhousing 150. This shape of printed circuit board 152 may self-align theboard within the housing. Printed circuit board 152 may also includecircuitry or other components for the operation of pressure sensor 112.Printed circuit board 152 may also include an opening that enableselectrical connection between printed circuit board 152 and othercomponents of pressure sensor 112. For example, printed circuit board152 may include an opening for feedthrough pin 154 to pass through fromcylindrical housing ferrule 156.

FIG. 7 is an exploded view of pressure sensor 112 of FIG. 6. As shown inFIG. 7, components of pressure sensor 112 include printed circuit board152, sensor housing 150, feedthrough assembly 162, and diaphragm 166.Some or all of these components may fit together to form the completedpressure sensor 112.

As discussed above, printed circuit board 152 may include one or moreopening 158 sized and shaped to accept feedthrough pin 154. Opening 158may be an aperture or other such void formed in printed circuit board152. Printed circuit board 152 may be sized and shaped to fit withinsensor housing 150. Sensor housing 160 may include housing ferrule 156and one or more protrusions 160. The one or more protrusions 160 mayprovide a slightly smaller inner diameter than housing ferrule 156 inorder to allow support structure 164 of feedthrough assembly 162 to tiltwithin housing ferrule 156. Support structure 164 may then be attachedto protrusion 160, e.g., via welding or any other appropriate mechanismfor securing support structure 164. The at least one protrusion 160 asdepicted in FIG. 7 is an annular ring or lip, however, protrusion 160may be a single protrusion or even a set of three or more protrusionscircumferentially spaced within housing ferrule 156 and aligned in aplane substantially orthogonal to an axis of the cylindrical housingferrule.

As shown in the example of FIG. 7, feedthrough assembly 162 includessupport structure 164, rigid insulator 184, and feedthrough pin 154.Feedthrough pin 154 may be coupled to substantially rigid insulator 184and may be electrically coupled to a capacitive plate (not shown) at abottom surface of rigid insulator 184. Substantially rigid insulator 184may be substantially rigid such that the capacitive plate (e.g. a metalcoating at a bottom surface of substantially rigid insulator 184)defines a reference plane with respect to deflectable diaphragm 166. Inthis manner, substantially rigid insulator 184 may be capable of someelastic deformation without incurring plastic deformation or fracture.However, it may be desirable for substantially rigid insulator 184 tosubstantially maintain its shape under operating conditions of pressuresensor 112.

Rigid insulator 184 may be mounted to support structure 164, and supportstructure 164 may be positioned within housing ferrule 156. Supportstructure 164 may be secured in a desired position within housingferrule 156 via one or more protrusions 160, e.g., by welding orotherwise securing support structure 164 to the one or more protrusions160. Diaphragm 166 may be attached to a distal edge of housing ferrule156. Diaphragm may function as a deformable capacitive plate forpressure sensor 112. Diaphragm 166 may be fixed along an entire edge toseal feedthrough assembly 162 within housing ferrule 156.

FIG. 8 is a conceptual diagram of a non-fluid contact side of oneexample of a pressure sensor 112. As shown in FIG. 8, pressure sensor112 includes sensor housing 150, printed circuit board 152, feedthroughpin 154, conductive ribbons 172 and 176, and contacts 170 and 174.Sensor housing 150 may be configured in an eccentric shape to allowpressure sensor 112 to self-align to a similarly shaped opening inbulkhead 104. Sensor housing 150 may also provide a recessed support forprinted circuit board 152 to be carried by sensor housing 150. Printedcircuit board 152 may also be shaped for self alignment with respect tosensor housing 150.

Printed circuit board 152 may provide electrical contacts 170 and 174.Contacts 170 and 174 may provide connection points on printed circuitboard 152 for conductive ribbons 172 and 176, respectively. Conductiveribbon 172 may electrically couples feedthrough pin 154 to contact 170.Also, conductive ribbon 176 may electrically couple sensor housing 150to contact 174. Sensor housing 150 may conducts electrical energybetween printed circuit board 152 and diaphragm 166 (of FIG. 7). Printedcircuit board 152 may also provide an opening 158 configured to receivefeedthrough pin 154.

Printed circuit board 152 may be configured in different shapes andsizes than those depicted in FIG. 8. In addition, multiple circuitboards may be housed within sensor housing 150. In some examples, two ormore conductive ribbons may be used in place of one or both ofconductive ribbons 172 and 176. Further, conductive ribbons 172 and 176may be replaced with different conductive structures that electricallycouple sensor housing 150 and feedthrough pin 154 to printed circuitboard 152. For example, conductive traces may be formed in printedcircuit board 152 that directly couple feedthrough pin 154 and sensorhousing 150. In other examples, any other electrically conductivestructure, such as a wirebond, may be utilized to electrically couplesensor housing 150 and feedthrough pin 154 to printed circuit board 152.Alternatively, a conductive epoxy may be used to secure printed circuitboard 152 and provide electrical conductivity between printed circuitboard 152 and sensor housing 150.

FIG. 9 is a conceptual diagram illustrating a perspective view from aninterior of a fluid enclosure of a fluid contacting side of a pressuresensor 112. As shown in FIG. 9, pressure sensor 112 includes sensorhousing 150 and diaphragm 166. Sensor housing 150 may include an outerflange 178 and an inner edge 180. Outer flange 178 may provide a shelfor lip to contact, or reside adjacent to, bulkhead 104. When sensorhousing 150 is placed within the opening of bulkhead 104, the outer edgeof outer flange 178 may be sealed to bulkhead 104 with a laser seam weldor a different type of attachment or bonding method. In this manner, thetop surface of outer flange 178 may be flush with bulkhead 104. In otherexamples, outer flange 178 may be larger than an opening in bulkhead 104such that outer flange 178 prevents pressure 112 from passing throughthe opening in bulkhead 104. In some examples, inner edge 180 maycontact a surface of bulkhead 104 to seal fluid within the fluidenclosure.

Diaphragm 166 is a deflectable capacitive plate of the capacitor used tomeasure pressure of fluid contacting diaphragm 166. Diaphragm 166 may besubstantially annularly shaped and may completely cover an openingdefined by housing ferrule 156 (not shown in FIG. 9). Diaphragm edge 182may correspond to an outer surface of housing ferrule 156 to form acontinuous outer surface of pressure sensor 112. Diaphragm 166 may beattached to housing ferrule 156 via welding, soldering, adhesives, orother attachment methods. In some examples, diaphragm edge 182 may notextend completely to the outer surface of housing ferrule 156. In otherexamples, diaphragm 166 may have a diameter larger than the outerdiameter of housing ferrule 156 such that diaphragm edge 182 folds overhousing ferrule 156.

Sensor housing 150 (including housing ferrule 156 not shown in FIG. 9)and diaphragm 166 may define an operative surface of pressure sensor112. The operative surface contacts the fluid within the fluid enclosurepartially defined by pressure sensor 112. In other examples, theoperative surface may only include diaphragm 166. Although diaphragm 166may be constructed as a solid structure or foil, diaphragm may beprovided in other configurations. For example, diaphragm 166 may beconstructed of multiple layers of the same material, layers of differentmaterials, or sandwiched layers of different materials. For example,diaphragm 166 may be constructed of an insulating material sandwiched bytwo conductive foil layers.

Sensor housing 150 and diaphragm 166 may be constructed of biocompatiblematerials and/or anti-corrosive materials because their surfaces comeinto contact with corrosive drugs, bodily fluids, or both. In someexamples, the materials may only need to be non-corrosive and compatiblewith pharmacological agents, and not biological agents, to functionwithin the example of FIG. 9 or other examples herein. In addition,these materials may be electrically conductive. Example materials mayinclude composite materials and metal alloys. Example metals or metalalloys may include aluminum, titanium, or nitinol. Example titaniumalloys include Grades 1, 2, 5, or 9. The titanium alloy used toconstruct diaphragm 166 may be electrically conductive, flexible enoughto deflect with increased pressure, able to resist plastic deformationor hysteresis, and able to resist cracking from cyclic deformation.Other materials that may be used alone or within an alloy may includegold, titanium, copper, niobium, nickel, aluminum, molybdenum, silver,or other such materials known in the art. A material used for diaphragm166 may be manufactured with a thinness that allows the diaphragm tomeet these performance requirements. Generally, the thickness ofdiaphragm 166 may be between 0.001 mm and 1.0 mm. More specifically, thethickness of diaphragm 166 may be between 0.02 mm and 0.13 mm. In oneexample, grade 9 titanium may be selected as the material for diaphragm166. Although the same material may be used in diaphragm 166 and sensorhousing 150, different materials may also be used. For example,different titanium alloys may be used.

Generally, a diameter of diaphragm 166 may be between approximately 3.0millimeters (mm) and 20 mm. More specifically, the diameter of diaphragm166 may be between 4.0 mm and 7.0 mm. In the example of FIG. 9,diaphragm 166 has a diameter of approximately 5.6 mm. A length ofpressure sensor 112 may be generally between 5.0 mm and 30 mm, and thewidth of pressure sensor 112 may be generally between 3.5 mm and 22 mm.In the example of FIG. 9, the length and width of pressure sensor 112may be approximately 10 mm and 7 mm, respectively. In other examples,pressure sensor 112 may be constructed of smaller or large dimensions,depending upon the desired application of pressure sensor 112.

FIG. 10 is a conceptual diagram illustrating a cross-section perspectiveview of pressure sensor 112. As shown in the example of FIG. 10,pressure sensor 112 includes sensor housing 150, printed circuit board152, electrical components 181, conductive ribbons 172 and 176,feedthrough pin 154, support structure 164, rigid insulator 184, rigidcapacitive plate 186, diaphragm 166, oil cup 188, and insulator bond190. When assembled, diaphragm 166 and rigid capacitive plate 186 mayform a capacitor that pressure sensor 112 utilizes to detect changes incapacitance caused by fluid pressure against diaphragm 166.

According to the example of FIG. 10, sensor housing 150 includes outerflange 178, housing ferrule 156, and at least one protrusion 160. Sensorhousing may also include a recessed support that accepts and secures aprinted circuit board 162 or other circuitry of pressure sensor 112.Although there may be a gap between sensor housing 150 and the edge ofprinted circuit board 152, some examples may not provide for any gapbetween the two structures. Outer flange 178 may be larger than theopening in bulkhead 104 to enable pressure sensor 112 to mate againstbulkhead 104. In the example of FIG. 10, outer flange 178 is shownaround a circumference of sensor housing 150, but in other examplesouter flange 178 may consist of one or more protrusions from sensorhousing 150.

As depicted in the example of FIG. 10, housing ferrule 156 is a portionof sensor housing 150 that surrounds and protects feedthrough assembly162. Housing ferrule 156 is cylindrical in shape, but housing ferrule156 may be constructed in other shapes as well. As depicted in theexample of FIG. 10, housing ferrule 156 has openings at both ends andprovides a mounting surface for diaphragm 166 at one end. In addition,at least one protrusion 160 provides a mounting point, or an attachmentsurface, for support structure 164 of feedthrough assembly 162 to besecured within housing ferrule 156. The at least one protrusion 160 maydefine a smaller inner diameter than housing ferrule 156, where thelarger inner diameter of housing ferrule 156 allows feedthrough assembly162 to be tilted to orient rigid capacitive plate 186 into a desiredposition.

The at least one protrusion 160 may be provided as an annular ring, alip, a single protrusion, or even a set of three or more protrusionscircumferentially spaced within housing ferrule 156 and aligned in aplane substantially orthogonal to an axis of cylindrical housing ferrule156. The at least one protrusion 160 may be integrally formed withhousing ferrule 156. In other examples, support structure 164 mayinstead provide the functional equivalent of protrusion 160 (e.g., oneor more protrusions on an outer surface of support structure 164) tomate with an inner surface of housing ferrule 156. The at least oneprotrusion 160 may be integrally formed with support structure 164. Inalternative examples, the at least one protrusion 160 may be a separatestructure configured to be attached to support structure 164 and aninner surface of housing ferrule 156.

Printed circuit board 152 may be inset within sensor housing 150.Printed circuit board 152 may carry circuitry used for operation ofpressure sensor 112. Printed circuit board 152 may also include otherelectrical components 181. Although, according to the example of FIG.10, electrical components 181 are shown extending from printed circuitboard 152, electrical components 181 may be recessed within printedcircuit board 152. In addition, opening 158 may formed in printedcircuit board 152. Opening 158 may allow nailhead 154A of feedthroughpin 154 to extend to or above a surface of printed circuit board 152 forconnection to, for example conductive ribbon 172. Nailhead 154A may beprovided as an attachment point for conductive ribbon 172. Nailhead 154Amay include an attachment surface having a larger diameter than theshaft of feedthrough pin 154. This attachment surface may also beconfigured to facilitate electrical coupling with conductive ribbon 172.Sensor housing 150 may conduct electrical current between diaphragm 166and printed circuit board 152 via conductive ribbon 176. In otherexamples, a conductive epoxy or other electrical conductive connectionsmay be used instead of conductive ribbon 176.

Feedthrough assembly 162 may be configured to be disposed within housingferrule 156. As shown in the example of FIG. 10, feedthrough assembly162 includes support structure 164, substantially rigid insulator 184,feedthrough pin 154, rigid capacitive plate 186, oil cup 188, andinsulator bond 190. Substantially rigid insulator 184 may benon-conductive and may provide a support for capacitive plate 186. Bynot conducting electricity, substantially rigid insulator 184 mayelectrically isolates capacitive plate 186 from any other electricallyconductive surface that may cause an undesirable short circuit. Rigidinsulator 184 may be substantially rigid and generally inflexible toretain its shape within pressure sensor 112, but rigid insulator 184 maybe capable of deforming to some degree. However, rigid insulator 184 maybe configured not to deform during normal operation of pressure sensor112 to maintain the metal coating in a reference plane with respect todeflectable diaphragm 166. Substantially rigid insulator 184 is shown ina cylindrical shape according to the example of FIG. 10, but theinsulator may be formed into other shapes as long as it provides asuitable surface for capacitive plate 186. Materials suitable forsubstantially rigid insulator may include ceramics, composite materials,polymers, or other electrically insulative materials.

According to the example of FIG. 10, capacitive plate 186 is disposed onsubstantially rigid insulator 184 and may be a metal alloy bondeddirectly to substantially rigid insulator 184. In one example,capacitive plate 186 is a gold braze that is directly bonded tosubstantially rigid insulator 104. In other examples, capacitive plate186 may be constructed by sputter coating, ion beam coating, chemicalvapor deposition, using an adhesive to join the metal alloy withsubstantially rigid insulator 184, or any other method known in the art.Capacitive plate 186 may also be constructed with layers of one or moredifferent metals. Example metals or metal alloys that may be used toconstruct capacitive plate 186 may include gold, titanium, copper,niobium, nickel, aluminum, molybdenum, silver, or any other suchmaterials known in the art. Although capacitive plate 186 does not coverthe entire surface of substantially rigid insulator 184 as shown in theexample of FIG. 10, capacitive plate 186 may cover the entire insulatorin other examples. Capacitive plate 186 may or may not be configured tobe rigid by itself. In some examples capacitive plate 186 may bearranged in a rigid position with respect to deflectable diaphragm basedon rigidity provided by substantially rigid insulator 184.

Capacitive plate 186 may be electrically coupled to pin end 154B offeedthrough pin 154. Capacitive plate 186 may fill a depression 194 ofrigid insulator 184 to create an oil cup 188. Oil cup 188 may be acollection of the same or similar material used to form capacitive plate186. When oil cup 188 is formed around pin end 154B, the metal alloy ofrigid capacitive plate 186 may bond to pin end 154B of feedthrough pin154. Since feedthrough pin 154 terminates at pin end 154B withindepression 194 of rigid insulator 184, feedthrough pin 154 is recessedfrom the capacitive surface of rigid capacitive plate 186. Therefore,the possibility that feedthrough pin 154 could cause a short circuitbetween capacitive plate 186 and diaphragm 166 by capacitive plate 186being closer to diaphragm 166 than desired may be minimized.Alternatively, a different conductive material than used to formcapacitive plate 186 may be used to create oil cup 188 and couple rigidcapacitive plate 186 and feedthrough pin 154.

Feedthrough pin 154 may be set away from a center axis of rigidinsulator 184 to minimize an impact of depression 194 on measuredcapacitance between diaphragm 166 and capacitive plate 186. In thismanner, the center axis of feedthrough pin 154 may not be shared withthe center axis of rigid insulator 184. In addition, an offset positionof feedthrough pin 154 may allow the use of different printed circuitboards with layouts accommodated by the ability to move the location offeedthrough pin by simply rotating feedthrough assembly 162 with respectto housing ferrule 156. However, feedthrough pin 154 may be located atany radial or circumferential position as long as feedthrough pin 154does not contact a conductive surface other than rigid capacitive plate186. Feedthrough pin 154 may be specifically configured to passelectrical current from rigid capacitive plate 186, through rigidinsulator 184, and to printed circuit board 152 without contacting otherconductive surfaces.

Rigid insulator 184 may be held in place by support structure 164.Support structure 164 may be a cylindrical collar that mounts rigidinsulator 184 to sensor housing 150. In other examples, supportstructure 184 may be comprised of multiple separate braces that mountrigid insulator 184 to sensor housing 150. Rigid insulator 184 may beattached to support structure 164 with insulator bond 190. Insulatorbond 190 may be an adhesive or melted alloy that is deposited around anoutside edge of rigid insulator 184 to bond rigid insulator 184 tosupport structure 164. In other examples, rigid insulator 184 may beattached to support structure 164 with pins, clamps, snap enclosures,pressure fit, or any other mechanical method to secure rigid insulator184.

Support structure 164 may be attached to sensor housing 150 via at leastone protrusion 160. The at least one protrusion 160 may extend from aninner surface of housing ferrule 156 to contact an outer edge of supportstructure 164. Support structure 164 may be welded or otherwise securedto the at least one protrusion 160. The at least one protrusion 160 mayallow feedthrough assembly 162 to tilt within housing ferrule 156 toorient rigid capacitive plate 186 in a desired plane with respect todiaphragm 166. Generally, the at least one protrusion 160 comprises lessthan 20 percent of a length of housing ferrule 156 between the distalend and the proximal end of housing ferrule 156, but the at least oneprotrusion 160 may have any height that still allows for the tilting offeedthrough assembly 162. Once support structure 164 is secured inplace, rigid capacitive plate 186 may be secured such that it does notmove relative to sensor housing 150.

Diaphragm 166 may operate as the second capacitive plate of capacitivepressure sensor 114. Diaphragm 166 may be attached to the distal edge ofhousing ferrule 156. Diaphragm 166 may be welded or soldered to housingferrule 156. In other examples, diaphragm 166 may be adhered or bondedto housing ferrule 156. Since diaphragm 166 is deflectable, or displayselastic deformation, diaphragm 166 may provide one or more indicationsof changing fluid pressure. When assembled, pressure sensor 112 maydefine a height “H” of a capacitive gap 192 between rigid capacitiveplate 186 and diaphragm 166 when no fluid pressure is exerted upondiaphragm 166. Capacitive gap 192 may also be referred to as a pick-offgap as known in the relevant arts. Generally, H is between approximately0.01 mm and 0.25 mm. In the example of FIG. 10, H is approximately 0.08mm. When the pressure increases against diaphragm 166, H will decreaseaccordingly. Although the gas filling capacitive gap 192 may be air,other inert or non-combustible gases may be used to fill this spacewithin pressure sensor 112. Alternatively, capacitive gap 192 may be avacuum.

FIG. 11 is a conceptual diagram illustrating the sensor housing 150 andan inside of housing ferrule 156. As shown in FIG. 11, sensor housing150 includes housing ferrule 156, at least one protrusion 160, and outerflange 178. Housing ferrule 156 includes an outer edge 198 that providesan attachment spot for diaphragm 166 (not shown). Housing ferrule 156also has an inner surface 196 that defines inner diameter D1. At leastone protrusion 160 extends inward from housing ferrule 156 to define aninner diameter D2. D1 is larger than D2 so that feedthrough assembly 162can be tilted within housing ferrule 156, but the at least oneprotrusion 160 is still close enough to support structure 164 forattachment to protrusion 160.

Generally, D1 may be between approximately 2.8 mm and 19 mm. Morespecifically, D1 may be between approximately 3.9 mm and 6.9 mm. In theexample of FIG. 9, D1 is approximately 5.0 mm. D1 may also be generally0.1 mm to 10.0 mm larger than D2 in the example of FIG. 9. In otherwords, the width of protrusion 160 is generally between 0.05 mm to 2.0mm. In the example of FIG. 9, D2 is approximately 4.6 mm. In otherexamples, D1 and D2 may be of smaller or larger dimensions, dependingupon requirements for positioning of feedthrough assembly 162.

In alternative examples, the at least one protrusion 160 may beconstructed as a part of support structure 164 instead of housingferrule 156. Therefore, housing ferrule 156 may have a single innerdiameter and support structure 164 provides one or more attachmentpoints that allow feedthrough assembly 162 to tilt within housingferrule 156 when orienting capacitive plate 186. For example, the atleast one protrusion 160 may take the form of an annular ring on theoutside of support structure 164. In any case, according to thisexample, feedthrough assembly 162 is provided the necessary space todefine the desired capacitive gap 192 between diaphragm 166 and rigidcapacitive plate 186.

FIG. 12 is a perspective diagram showing a perspective view of thecapacitive plate side of feedthrough assembly 162. As shown in FIG. 12,feedthrough assembly 162 includes support structure 164, rigid insulator184, capacitive plate 186, and insulator bond 190. Support structure 164is bonded to rigid insulator 184 with insulator bond 190 around theentire circumference of rigid insulator 184. Insulator bond 190 may beformed in a manner in which the material settles down between rigidinsulator 184 and an inner surface of support structure 164 to securethe components together. Insulator bond 190 may be formed by placingrigid insulator 184 within support structure 164 and positioning a ringof material, e.g., gold, silver, copper, molybdenum, or other materialknown in the art, around rigid insulator 184 and above support structure164. Feedthrough assembly 162 is then heated until the material meltsand flows down between rigid insulator 184 and support structure 164.This settling and forming of insulator bond 190 may shift or raise rigidinsulator 184 from support structure 164. In this manner, rigidinsulator 184 may be secured in a plane no longer parallel to the planeformed by support structure 164.

Capacitive plate 186 is deposited on the surface of rigid insulator 184.As shown in the example of FIG. 12, capacitive plate 186 may be a metalalloy that does not cover the entire surface of rigid insulator 184.This smaller diameter of rigid capacitive plate 186 may prevent anyelectrical interference between rigid capacitive plate 186 and insulatorbond 190. Although capacitive plate 186 may have a uniform thickness,some variation in a thickness of the deposited metal alloy may bepresent due to manufacturing process variations. However, an effectcaused by any non-uniformities in capacitive plate 186 may be minimizeddue to the assembly process for pressure sensor 112 described herein.

FIG. 13 illustrates a perspective view of a cross-section of feedthroughassembly 162. Similar to example shown in FIG. 10, FIG. 13 shows thatfeedthrough assembly 162 includes feedthrough pin 154, support structure164, rigid insulator 184, rigid capacitive plate 186, diaphragm 166, oilcup 188, and insulator bond 190. In addition, FIG. 13 shows bond layer200 and proximal end 202 of support structure 164. Proximal end 202 ofsupport structure 164 may be used to mount feedthrough assembly 162 tosensor housing 150. More specifically, proximal end 202 may be weldeddirectly to at least one protrusion 160 inside of housing ferrule 156.

Bond layer 200 may be a layer or film created between support structure164 and rigid insulator 184. Bond layer 200 may be formed by directlyplacing the adhesive or material between these structures.Alternatively, bond layer 200 may be formed when the amorphous materialis applied to create insulator bond 190 and a portion of the materialfills a gap between support structure 164 and rigid insulator 184.During manufacturing, bond layer 200 may cause rigid insulator 104 to bedisplaced from the surfaces of support structure 164 so that rigidcapacitive plate 186 is no longer square with support structure 164.This tilting or slanting of rigid insulator 184 may be substantiallynegligible when pressure sensor 112 is assembled according to techniquesdescribed herein. For example, at least one protrusion 160 may allowsupport structure 164 to be tilted within housing ferrule 156 to orientcapacitive plate 186 to a desired plane substantially parallel to aplane of diaphragm 166.

FIG. 14 is a conceptual diagram illustrating an assembly tool 210 thatmay be used to define a capacitive gap between capacitive plate 186 anddiaphragm 166. As shown in FIG. 14, assembly tool 210 includes baseplate 206 and stage 208 raised from base plate 206. A height of stage208 above a top surface of base plate 206 may be equivalent to acapacitive gap 192 created between the two capacitive plates of thecapacitor. In this manner, stage 208 may define a plane parallel to theplane of base plate 206 so that capacitive gap 192 is substantiallyuniform.

Housing ferrule 156 of sensor housing 150 may be placed around stage 208such that a distal edge of housing ferrule 156 contacts a top surface ofbase plate 206. The distal edge of housing ferrule 156 may be an edgefurthest from the rest of sensor housing 150. Feedthrough assembly 162may be placed within housing ferrule 156 such that that capacitive plate186 contacts stage 208. Capacitive plate 186 may contact stage 208 suchthat it is substantially flush with stage 208. By contacting stage 208,capacitive plate 186 may be oriented in a plane substantially parallelto a plane created by the distal edge of housing ferrule 156.Feedthrough assembly 162 may also be circumferentially oriented toposition feedthrough pin 154 appropriately within pressure sensor 112.

In some cases, feedthrough assembly 162 may need to be tilted withinhousing ferrule 156 to properly seat capacitive plate 186 to stage 208.In one example, rigid insulator 184 may have been lifted or offsetslightly from support structure 164. In another example, capacitiveplate 186 may have varying thickness across the plate due tomanufacturing defects. Ferrule gap 204 is provided to enable thistilting to occur while allowing proximal end 202 of support structure164 to contact the at least one protrusion 160 for attachment to sensorhousing 150. Upon removal of assembly tool 210, diaphragm 166 may beattached, e.g., welded, to the distal edge of housing ferrule 156.

Stage 208 as shown in FIG. 14 is generally cylindrical in shape, butstage 208 may be configured in any shape that fits within housingferrule 156 and creates a plane. In other examples, stage 208 may becomprised of three or more separate protrusions from base plate 206 thatform a plane parallel to the top surface of base plate 206. The heightof stage 208 from the top surface of base plate 206 may be generallybetween 0.01 mm and 0.25 mm. In the example of FIG. 14, stage 208 mayhave a height of approximately 0.08 mm.

FIG. 15 is a flow diagram describing an example method for mountingfeedthrough assembly 162 within pressure sensor 112 and attachingdiaphragm 166. As shown in FIG. 15, assembly tool 210 is placed on asurface with stage 208 facing upwards (220). Next, housing ferrule 156of sensor housing 150 is set over stage 208 such that the distal edge ofhousing ferrule 156 contacts the top surface of base plate 206 (222).

Feedthrough assembly 162 is then inserted into housing ferrule 156 sothat rigid capacitive plate 186 contacts stage 208 (224). This seatingprocess may also involve pressing rigid capacitive plate 186 againststage 208. Feedthrough assembly 162 is then circumferentially orientedto sensor housing 150 to allow feedthrough pin 154 to pass throughopening 158 in printed circuit board 152 (226). Once oriented, supportstructure 164 of feedthrough assembly 162 is welded to protrusion 160 ofhousing ferrule 156 (228). Assembly tool 210 is then removed fromhousing ferrule 156 (230) and diaphragm 166 is welded into the distaledge of housing ferrule 156 (232).

FIG. 16 is a flow diagram illustrating an example technique fororienting pressure sensor 112 within bulkhead 104 of IMD 16. As shown inFIG. 16, pressure sensor 112 is first assembled according, for example,the method of FIG. 15 (234). Once assembled, the opening for pressuresensor 112 is located in bulkhead 104 (236). Pressure sensor 112 is thenplaced into the opening of bulkhead 104 (238). Since pressure sensor 112is configured as a shape that is self-aligning to the opening, there isonly one way that pressure sensor 112 will fit within the opening ofbulkhead 104.

Once pressure sensor 112 is in place, sensor housing 150 of pressuresensor 112 is welded into bulkhead 104 to further define the fluidenclosure (240). Next, bulkhead 104 is attached (e.g., welded) toreservoir back housing 102 to complete the fluid enclosure (242).Additional pressure sensors 112, such as a pressure sensor near refillport 28, may be added to bulkhead 104 or other fluid enclosures in thesame self-aligning manner.

FIG. 17 is a flow diagram illustrating an example method for detecting achange in fluid quantify with pressure sensor 112. IMD 16 is initiallyset to operate for drug delivery (246). Drug delivery includes thedelivery of fluid from IMD 16 as determined by an automated program oras requested by patient 12. Once IMD 16 is to deliver fluid, IMD 16releases a bolus, or dose, of fluid from reservoir 122 that defines thereservoir of drug (248). In other examples, IMD 16 may release fluid ata controlled rate over an extended period of time instead of a bolus ordose of fluid at one time. Usually, medical pump 38 expels the requestedamount of fluid.

Upon the release of fluid bolus, pressure sensor 112 detects theresulting pressure within reservoir 122 proximate to the release valve118 (250). The pressure may be indicative of the quantity and/or flowrate of fluid delivered to patient 12. This information may be used toconfirm the identified amount and rate of fluid that medical pump 38 wasexpected to deliver to patient 12. IMD 16 may then store, process,communicate, or otherwise use the output of pressure sensor 112.

In some examples, differences between the detected pressure changes andrequested medical pump 38 actions may elicit an alert to programmer 20.Any differences may indicate that medical pump 38 is malfunctioning,there is a clog in catheter 18, or there is some other problem with IMD16. In other examples, pressure sensor 112 may be used in closed-loopfeedback control of medical pump 38. Alternatively, pressure sensor 112may be used to monitor the refilling of fluid into IMD 16.Above-threshold indications of pressure may be important to limitingdamage to IMD 16 or the direct delivery of drug into patient 12 tissues.

The disclosure describes a device that may be capable of providing manyfeatures. For example, the pressure sensor itself forms part of thefluid enclosure to prevent intermediary structures between the fluid andthe pressure sensor. This modular construction can increase pressuresensor performance while reducing manufacturing time and costs. Also,the fluid enclosure may be constructed with a uniform corrosionresistant and/or biocompatible fluid contact surface to limit fluid tosurface interactions that may cause corrosion or other problems. Thepressure sensor may also include a conductive diaphragm directly weldedto the housing to eliminate adhesives or other less robust attachingmechanisms from being used. The pressure sensor may also provide acapacitive plate that is directly adhered to a supporting rigidinsulator without adhesives or bonding materials. As an additionalexample, the pressure sensor may include a feedthrough pin that isrecessed from the capacitive plane of the metal coating on the insulatorto eliminate and/or reduce a possibility of undesirable short circuitsbetween two capacitive plates of the pressure sensor.

The disclosure may also provide further features. For example, at leastone protrusion may be defined within a housing ferrule to create a gapbetween the housing ferrule and a support structure of a capacitiveplate and provide an attachment structure between these two components.This gap may allow the support structure to be tilted or oriented suchthat the capacitive plate can be mounted in a desired plane. Thisprotrusion may be part of the housing ferrule or the support structure.As another example, an assembly tool may include a stage of apredetermined height to set one capacitive plate at a desired positionand plane within the housing ferrule. In this manner, discrepanciescaused by manufacturing inconsistencies with respect to the capacitiveplate, insulator, and supporting structure with respect to a desiredposition for the capacitive plate may be reduced or eliminated.

The techniques described in this disclosure may be implemented, at leastin part, in hardware, software, firmware or any combination thereof. Forexample, various aspects of the techniques may be implemented within oneor more microprocessors, digital signal processors (DSPs), applicationspecific integrated circuits (ASICs), field programmable gate arrays(FPGAs), or any other equivalent integrated or discrete logic circuitry,as well as any combinations of such components, embodied in programmers,such as physician or patient programmers, stimulators, or other devices.The term “processor” or “processing circuitry” may generally refer toany of the foregoing logic circuitry, alone or in combination with otherlogic circuitry, or any other equivalent circuitry.

In addition, it should be noted that the systems described herein maynot be limited to treatment of a human patient. In alternativeembodiments, these systems may be implemented in non-human patients,e.g., primates, canines, equines, pigs, and felines. These animals mayundergo clinical or research therapies that may benefit from the subjectmatter of this disclosure.

Many examples of the disclosure have been described. Variousmodifications may be made without departing from the scope of theclaims. These and other examples are within the scope of the followingclaims.

1. A pressure sensor, comprising: a housing ferrule defining a firstinner diameter, wherein the housing ferrule is configured to receive afirst capacitive plate of a capacitor; and at least one protrusiondisposed within the housing ferrule that defines a second inner diametersmaller than the first inner diameter, wherein: the at least oneprotrusion is configured to provide a mounting point between the housingferrule and a support structure of the first capacitive plate; thehousing ferrule and the support structure define a gap when the at leastone protrusion is used to secure the support structure to the housingferrule; and the housing ferrule is configured to support a secondcapacitive plate substantially parallel to the first capacitive platewithin the housing ferrule.
 2. The pressure sensor of claim 1, whereinthe gap allows the support structure to be tilted such that the firstcapacitive plate can be oriented in a first plane substantially parallelto a second plane of a second capacitive plate.
 3. The pressure sensorof claim 1, wherein the first inner diameter is generally between 0.1 mmand 10.0 mm larger than the second inner diameter.
 4. The pressuresensor of claim 3, wherein the first inner diameter is approximately 0.4mm larger than the second inner diameter.
 5. The pressure sensor ofclaim 1, wherein the at least one protrusion comprises less than 20percent of a ferrule length between a proximal end and a distal end ofthe housing ferrule.
 6. The pressure sensor of claim 1, wherein the atleast one protrusion is formed integral with the housing ferrule.
 7. Thepressure sensor of claim 1, wherein the at least one protrusion isformed integral with the support structure.
 8. The pressure sensor ofclaim 1, wherein the at least one protrusion comprises at least threeprotrusions spaced circumferentially within the housing ferrule andaligned in a plane substantially orthogonal to an axis of the housingferrule.
 9. The pressure sensor of claim 1, wherein the at least oneprotrusion is a substantially annular ring.
 10. The pressure sensor ofclaim 1, wherein the support structure is configured to be welded to theat least one protrusion.
 11. A method for assembling a pressure sensor,the method comprising: placing a first capacitive plate and a supportstructure attached to the first capacitive plate within a housingferrule defining a first inner diameter; tilting the support structurewithin the housing ferrule to orient the first capacitive plate in afirst plane substantially parallel to a second plane of a secondcapacitive plate; securing the support structure to the housing ferrulevia at least one protrusion, wherein the at least one protrusion definesa second inner diameter smaller than the first inner diameter; andmounting the second capacitive plate to the housing ferrule.
 12. Themethod of claim 11, wherein placing the first capacitive plate and thesupport structure attached to the first capacitive plate within thehousing ferrule includes defining a gap between the housing ferrule andthe support structure, wherein the gap allows the support structure totilt within the housing ferrule.
 13. The method of claim 11, furthercomprising: contacting the housing ferrule against a base plate of anassembly tool, wherein tilting the support structure comprisescontacting the first capacitive plate against a stage of the assemblytool.
 14. The method of claim 11, further comprising: circumferentiallyorienting the first capacitive plate according to a position of afeedthrough pin coupled to the first capacitive plate and configured toextend through an aperture of a printed circuit board.
 15. The method ofclaim 11, wherein securing the support structure to the housing ferruleincludes securing the support structure via at least one protrusionintegrally formed with the housing ferrule, and wherein securing thesupport structure to the housing ferrule comprises: welding the supportstructure to the at least one protrusion within the housing ferrule. 16.The method of claim 11, wherein securing the support structure to thehousing ferrule via at least one protrusion includes securing thesupport structure via at least one protrusion integrally formed with thesupport structure, and wherein securing the support structure comprises:welding the at least one protrusion to the housing ferrule.
 17. Themethod of claim 11, wherein securing the support structure to thehousing ferrule includes securing the support structure via at leastthree protrusions spaced circumferentially within the housing ferruleand aligned in a plane substantially orthogonal to an axis of thehousing ferrule.
 18. The method of claim 11, wherein securing thesupport structure to the housing ferrule includes securing the supportstructure via a substantially annular ring.
 19. The method of claim 11,further comprising: welding the second capacitive plate to an edge ofthe housing ferrule, wherein the second capacitive plate is a titaniumdiaphragm.
 20. A pressure sensor assembly tool, the tool comprising: abase plate; and a stage raised from the base plate and configured to:fit within a housing ferrule to allow an edge of the housing ferrule topass the stage and contact a top surface of the base plate; and set auniform gap between a diaphragm plane defined by the edge of the housingferrule and a capacitive plate mountable within the housing ferrule. 21.The tool of claim 20, wherein the stage height from the top surface ofthe base plate is generally between 0.01 mm and 0.25 mm.
 22. The tool ofclaim 20, wherein the stage height from the top surface of the baseplate is approximately 0.08 mm.
 23. The tool of claim 20, wherein: thestage is cylindrical in shape; and a top surface of the cylindricalstage is substantially parallel to the top surface of the base plate.24. The tool of claim 20, wherein: the stage comprises at least threeseparate protrusions from the base plate; and the at least threeseparate protrusions form a plane substantially parallel to the topsurface of the base plate.
 25. The tool of claim 20, wherein: thecapacitive plate is coupled to a support structure; and the stage isconfigured to position the support structure within the housing ferrulesuch that the support structure can be secured to the housing ferrulevia at least one protrusion within the housing ferrule.
 26. A method forassembling a pressure sensor, the method comprising: contacting an endof a housing ferrule to a base plate of an assembly tool, wherein thehousing ferrule surrounds a stage of the assembly tool; placing a firstcapacitive plate and attached support structure within the housingferrule; placing the first capacitive plate against the stage to orientthe first capacitive plate in a first plane parallel to a second planedefined by the stage; securing the support structure to the housingferrule; and mounting a second capacitive plate to the housing ferruleafter removing the assembly tool.
 27. The method of claim 26, whereinthe first capacitive plate and attached support structure are configuredto be tilted within the housing ferrule such that the first capacitiveplate can be arranged substantially flush with the stage.
 28. The methodof claim 26, wherein securing the support structure to the housingferrule comprises welding the support structure to at least oneprotrusion within the housing ferrule, wherein the at least oneprotrusion defines a second inner diameter smaller than a first innerdiameter of the housing ferrule.
 29. The method of claim 26, furthercomprising circumferentially orienting the first capacitive plateaccording to a location of a feedthrough pin coupled to the firstcapacitive plate and configured to extend through an aperture of aprinted circuit board.
 30. The method of claim 26, further comprising:removing the assembly tool from the housing ferrule; and welding atitanium diaphragm to the first end of the housing ferrule, wherein thetitanium diaphragm is a second capacitive plate parallel to the firstcapacitive plate.